Marin County wetlands rise again in Hamilton airfield restoration

Water flows across runway in Novato as restoration brings back marsh habitat

A backhoe digs out a levee at the old Hamilton Field in Novato, opening up a channel for water to flood the base.

A backhoe digs out a levee at the old Hamilton Field in Novato, opening up a channel for water to flood the base.

Photo: Michael Short, The Chronicle

Photo: Michael Short, The Chronicle

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A backhoe digs out a levee at the old Hamilton Field in Novato, opening up a channel for water to flood the base.

A backhoe digs out a levee at the old Hamilton Field in Novato, opening up a channel for water to flood the base.

Photo: Michael Short, The Chronicle

Marin County wetlands rise again in Hamilton airfield restoration

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A cheer went up as salt water from San Pablo Bay poured through a breached levee Friday and flooded old, abandoned Hamilton Field in Novato, a landmark moment in the effort to restore Bay Area marshland habitat.

The levee breach was the last, biggest step in nearly two decades of work by conservationists to reconnect 648 acres - about 1 square mile - of wetlands to the bay and to restore tideland habitat for shorebirds, waterfowl, fish and wildlife.

The flooding of the runway at the former Air Force base, which was closed starting in 1973, is part of a regional effort to restore 100,000 acres of former wetlands around San Francisco Bay, according to conservationists. The Hamilton area was diked off around the turn of the 19th century, cutting off a primary landing spot for thousands of migrating waterfowl along the Pacific Flyway. It had remained dry until Friday, when a backhoe dug out the remaining mud barrier.

"It's actually very emotional for me to see this piece of land that has been disconnected from the bay for at least a century connected again," said Sam Schuchat, the executive officer for the California State Coastal Conservancy, which is jointly handling the project with the U.S. Army Corps of Engineers. "Now, as the years go by, as the seasons go by, we'll be able to watch this landscape change."

The bay water began seeping through as the last chunk of mud was pushed out of the way during high tide Friday. Within seconds, water was rushing through the breach, flowing like a river through the man-made channel onto a portion of the airfield already covered with water from recent rains and runoff that was deliberately pumped in. The wetlands will fill up and recede with the tides, said Tom Gandesbery, the project manager, but it will take 10 or 20 years for it to become a salt marsh. The trick now, he said, is to wait and watch the marsh vegetation grow.

Creating the new tidal marsh, which cost $107 million over 10 years, involved more than just letting in the water, Schuchat said. Draining the land had caused it to subside, he said, so 5.6 million cubic yards of dredged mud had to be brought in to raise the land to its natural height. Volunteers and students planted native vegetation and grew tens of thousands of plants on the imported material, three quarters of which came from dredging at the Port of Oakland.

Habitat for many species

Schuchat said the area was engineered in a manner that would create different habitats, including tidal marshland and brackish and freshwater wetlands. The restored area, which includes a 3-mile section of the Bay Trail, will provide crucial habitat for endangered and threatened species, including steelhead trout, salmon, California clapper rail, black rail, brown pelican and salt marsh harvest mouse, Schuchat said.

"This was designed with sea-level rise, climate change and ecological resiliency in mind," said Rep. Jared Huffman, D-San Rafael. "This is also a model project for reuse of our resources."

Hundreds of thousands of acres of marshland once lined San Francisco Bay and the delta, but about 85 percent of the historic habitat was drained, dried out for farmland or paved over for urban development. The airstrip in Novato was built on the dried-out wetlands in the 1920s and was named Hamilton Field in 1932.

The first planes at Hamilton were B-10 and B-12 bombers. Later came the big bomber known as the Boeing B-17 Flying Fortress. The site became an Army Air Corps fighter base in 1940. Fighters were sent from Hamilton to Oahu to defend Americans during the Japanese attack on Pearl Harbor, triggering the United States' entry into World War II. The Enola Gay bomber is said to have made a stop at Hamilton on its way to drop the atomic bomb on Japan in 1945.

Long cleanup process

The Air Force curtailed activities at the base in 1973, but units were still housed there until 1976, when base operations ended. The Army and Navy conveyed the property to the Coastal Conservancy, and the old base has been transformed over the past decade into a large community with homes and businesses in restored military buildings. Restoration of the land, which included cleanup of fuel, methane, and other toxic substances on the airfield and around the base, has been going on since 1996.

Schuchat said the conservancy will now turn its attention toward restoring 1,850 acres north of the airfield, including a large portion of Bel Marin Keys, an unincorporated community in Marin County. It is part of what he called a "renaissance" of bay wetlands restoration going on right now, including 900 acres at Sears Point in Sonoma County, 600 acres in Vallejo, 10,000 acres of former salt ponds in the Napa-Sonoma Marsh and 15,000 acres of salt ponds in the South Bay.

Ambitious goal

Conservationists are well on their way to meeting the 100,000-acre wetlands goal, which Schuchat said will ultimately cost $1.5 billion to complete.

"It's good to see the first big phase of wetlands restoration done," Gandesbery said. "This was a harder one to do because this was a closed military base, so they had to clean it up first."